In a medium-sized bowl, mix; milk, mayonnaise, apple cider vinegar, brown sugar, salt, pepper, and Onion powder. Stir until well blended using a whisk. Set aside.
In a large pot, boil the pasta shells according to package directions and drain. You want soft shells that will absorb the flavor of the dressing. Al dente shells are not recommended for this recipe.
Allow your cooked shells to cool.
Dump the cooled pasta shells into a large bowl. Pour all but 1/2 cup of the dressing over the pasta shells and stir.
Now add the celery and carrot sticks. Fold into the pasta with the dressing until mixed well.
Pour the remaining dressing into the pasta salad mixture and stir to blend well. Cover and chill for at least one hour in the refrigerator before serving.
This Hawaiian Pasta Salad can be made one day ahead and stored, covered in the refrigerator before serving.